If your PHP files suddenly stop working for no apparant reason and you just get a blank page for all your PHP files then the first thing you will do is to check your error_log. And if you have repeating lines in your error log such as "PHP Warning: Unknown(): Unable to load dynamic library '/usr/local/php4/lib/php/extensions/no-debug " then you can solve it.
Goto your hosting control panel. Assuming you have hosted with hostmonster, login to your control panel. Under "Software/services" section, click on the PHP config icon to enter into the PHP configuration.
Here you will see three options, PHP5, PHP5 single ini and Fast CGI. If I am not wrong you have probably chosen Fast CGI option before. Now just change it back to PHP5 option and click 'Save Changes' button.
There you go. Refresh your PHP page and you should see it working.